I've noticed 2 instances of usage of a the prefix where it doesn't seem to correspond with standard usage of English.
The flu
I'd expect a flu or just flu:
- He caught a flu
- She's infected with flu
- They have flu
Instead, the common usage seems to be the flu, such as Is It a Cold or the Flu? How to Tell the Difference or Dispelling misinformation about the flu vaccine (with more examples inside).
The movies
Mid-way of writing my argument for this one, I've noticed it had been asked and answered, albeit I was not convinced why "the movies" as a way to describe walking to a cinema to watch a movie, stayed as an idiomatic phrase today (a relic from a past usage of "moving pictures") and wasn't replaced by the simpler, singular form of a movie.
Happy to hear your thoughts for this one here or in the original thread.